Revision 531029: /head/Mk/Scripts/do-depends.sh
When building a port with make DEBUG_MK_SCRIPTS=1
                     or   make DEBUG_MK_SCRIPTS_FIND_LIB=1
when Mk/Scripts/do-depends.sh is called 
[ -n "${DEBUG_MK_SCRIPTS}" -o -n "${DEBUG_MK_SCRIPTS_FIND_LIB}" ] && set -x
and the shell tracing works as expected. (set -x)

However, when do-depends.sh calls sub-script: Mk/Scripts/find-lib.sh
there is no shell tracing for find-lib.sh

I believe the the cause is in Mk/Scripts/do-depends.sh
find_lib()
{ ... 
  libfile=$(env -i PATH="${PATH}" LIB_DIRS="${dp_LIB_DIRS}" LOCALBASE="${dp_LOCALBASE}" ${dp_SH} ${dp_SCRIPTSDIR}/find-lib.sh $1)
  ...
}

When ports calls Mk/Scripts/do-depends.sh
from: Mk/bsd.port.mk
it is using:   ${SETENV} \
            		dp_RAWDEPENDS="${${deptype}_DEPENDS}" \
            		dp_DEPTYPE="${deptype}_DEPENDS" \
                             ...
                        ${SH} ${SCRIPTSDIR}/do-depends.sh

SETENV = /usr/bin/env

NOTE: I tried to use the 'preview' tab but it does not seem to be working,
      only get a blank description box.